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Fluid condition monitoring can be used to assess not only the condition of hydraulic oil, but also of the engine

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Fluid condition monitoring can be used to assess not only the condition of hydraulic oil, but also of the engine. Service intervals can then be matched to the actual condition of the machine. Results from the analysis can be used to extend the life of engines and hydraulic systems and predict faults before they occur. Experience at the Port of Tacoma, Wash., epitomizes this concept.

A potential for savings

Much of the yard equipment at the Port of Tacoma is owned and operated by the port authority or leased to private stevedores. Each machine operates for 200 to 2500 hours annually. In an attempt to reduce maintenance and extend the life of its container handling straddle carriers, Figure 1, authority officials first experimented with hydraulic fluid testing in 1994.

Initially, a testing system was tried with the hydraulic fluid on two older Drott hydrostatic straddle carriers and two Kalmar lift trucks. The straddle carriers are huge machines, which becomes evident when observing the size of the man standing at far left in the picture. These carriers operate at pressures to 4000 psi and have two 75-gal reservoirs supplying Dynapower piston pumps, manufactured by Eaton Hydraulics. The lift trucks have a lower operating pressure of 2900 psi and 80-gal tanks fitted with Vickers piston pumps. The oil used is Chevron AW MV ISO 46 hydraulic fluid.

Particle counting

The first step was to assess the contamination of the hydraulic fluid by particle counting, which detects the size and quantity of contaminants in the fluid. The framework is provided by ISO 4406, which gives two measures: the total number per ml of particles 5-µm and greater in size and 15-µm or greater. This is expressed as two numbers, for example 17/15, each of which denotes a range of the actual number of particles (see Table 1, below).

Based on the experience of our oil analysis department, the port authority officials determined that the target cleanliness level for the straddle carriers and lift trucks should be 14/11 and 15/13 respectively, the difference reflecting, among other conditions, the higher operating pressure of the straddle carriers.

The first test results revealed particle counts for the straddle carriers of 20/15 and 20/16 the lift trucks came in at 21/15 and 21 /16. We estimated that the life of the hydraulic systems could be extended by three and a half times on the lift trucks and four to five times on the straddle carriers by reducing the amount of particulate contamination.

Benefits of success

The next step was to improve the hydraulic systems' filtration systems. We installed a depth-type kidney loop filtration system (including a low flow rate filter with a high particle capture performance) on each machine— a total cost of about $1500 per lift truck and $5000 per straddle carrier.

The initial results were very impressive: particle counts dropped to the target levels, and some tests returned results as low as 10/9. Not surprisingly, annual maintenance costs subsequently fell by 45% on one straddle carrier and by 97% on the other. This machine had been costing Port of Tacoma $45.52 per operating hour just in maintenance costs!

Similar benefits were gained with the lift trucks. They exhibited a 65% to 71% decline in particle count, with maintenance costs per operating hour down to 77¢ for one machine and 86¢ for the other.